AbstractHelicases are ubiquitous enzymes involved in nucleic acid metabolism. The PcrA DNA helicase is an essential bacterial protein involved in rolling circle plasmid replication and DNA repair. Recent crystal structures of PcrA bound to DNA indicate that a flexible loop mediates a functionally important rigid‐body‐domain rotation. In this study, we report stochastic boundary molecular dynamics simulations focused on this region for wild‐type and mutants designed to increase the rigidity of the region. Residues in the region that were helix‐disfavoring, such as glycine, threonine, and others, were mutated to alanine. The simulated dynamics, analyzed with a variety of measures of structure and mobility, indicate that a few point mutations will substantially increase helix formation in this region. Subnanosecond stochastic boundary molecular dynamics simulations at several temperatures offer a rapid protocol for assessing large numbers of mutants and provides a novel strategy for the design of experiments to test the role of this flexible loop region in the function of PcrA. Proteins 2003;52:254–262. © 2003 Wiley‐Liss, Inc.